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Yes, this is a rebuilt 351 replacing the 302. The engine vacuum readings I posted is current, around 18 in. at idle. I rebuilt this engine in Missouri closer to sea level and vacuum was 21 in. there. The needle is steady at idle, just a very slight movement. The vacuum readings are picture perfect to the first two examples of a "Normal" motor found here: TRS Magazine - Dealing with engine vacuum
I replaced the new plugs that were put in for first start up a couple weeks ago with another new set, which are already fouling. I'm now on my 2nd set of plugs with only 2,500 miles on engine. Both sets are Autolite coppers for a late 90's Explorer with GT40P heads.
I like the idea of putting the stock rockers back on before tearing heads off and seeing how it runs.
Perhaps these plugs are fuel fouled and oil fouled? I don't know if the fouled O2 sensor is a result of the engine issues or if the O2 sensor is to blame. I am stumped at this point and appreciate all the help and ideas I can get!
As goinboarding stated, the baffle in the valve cover is very important. Pull the PCV hose and see if oil is dripping out of it. Did you move the PCV location?
Did you install the rings? If so, did you stagger the ring gap, especially on the oil control rings?
Did you check for cylinder taper? Did you check ring end gap?
Well I see what's going on now. I peaked behind the throttle body plates and there's a big puddle of fresh, clean oil collected on the bottom of the upper intake manifold. The PCV system must be sucking oil up through there and being sucked into the combustion chamber. The old 351 had a round, hockey puck piece of plastic coming out of the valve cover, then a hose to the PCV valve, and then into the manifold. I deleted the hockey puck and ran the valve out of the cover and then a hose to manifold like the 302 setup. What is this piece called and would it be the cause of my problem? It looks like the stock 351 setup had a plastic elbow, hose, valve, then hose to manifold.
As goinboarding stated, the baffle in the valve cover is very important. Pull the PCV hose and see if oil is dripping out of it. Did you move the PCV location?
Did you install the rings? If so, did you stagger the ring gap, especially on the oil control rings?
Did you check for cylinder taper? Did you check ring end gap?
PCV is in same location, but I removed the "hockey puck" (Breather?) and routed everything like the 302. I just pulled the PCV valve, and it does indeed have oil dripping out of it. Any other reason as to why it's sucking so much oil up into the upper manifold?
I did install the rings. They were clocked and checked for tape and end gap.
PCV is in same location, but I removed the "hockey puck" (Breather?) and routed everything like the 302. I just pulled the PCV valve, and it does indeed have oil dripping out of it. Any other reason as to why it's sucking so much oil up into the upper manifold?
I did install the rings. They were clocked and checked for tape and end gap.
Am I correct, - you do not still have the breather in place? Is the PCV valve sitting in the valve cover like a BIG vacuum cleaner hose, with no baffle between that and the oil from the push rods/rocker arms?
If so, install the ( hockey puck ) or switch valve covers if the other one has the baffle. Remove the plugs and clean them all ( when you get the double joint spark plug socket ) with carb cleaner and rinse with brake clean. Reinstall them and see what happens. Remove the puddle of course from the intake plenum. Clean all the oil from the PCV valve and hose also.
Before you start the engine, temporarily put a piece of an old white t-shirt over the "exit" end of the PCV valve and reassemble the hose, run the engine for a few minutes, remove the piece of t-shirt, and see if it is still sucking up oil. The t-shirt piece may have a small amount of oil on it but it shouldn't be saturated.
Correct, the breather has not been in place since this engine has been installed in my vehicle. The 302 did not have a breather so I just routed everything like that. I looked down the hole in valve cover just now and there appears to be a baffle, but I suppose the breather still needs to installed. I don't see this breather on stock 351's or 302's for this model and vintage however. But there definitely is a lot of oil in PCV valve and hose and big puddle collecting on bottom of upper intake plenum. Is there any other reason why oil is being sucked through the valve and into intake that I may be overlooking? I'll get a hold of a new breather and will clean everything up as you suggested as see what happens.
I just wanted to make sure you had the baffles in place. If you pull the oil fill cap while it's running, is there vacuum there, at the valve cover?
Yes, oil fill cap removed and breather hose from air intake to fill cap plugged, it was pulling vacuum. Not sure if thats a good thing or not, or perhaps I performed test incorrectly? But it's definitely pulling vacuum.
The idea with disconnecting the MAF meter is to see if the computer is in limp mode or not, so you want to do this on a warmed up motor. If disconnecting it makes no difference at all to the way the engine runs then you now know the computer is ignoring it, and that means something is forcing the computer into this state and your problem is EFI system related. But if disconnecting it does make a difference then you know the computer is trying to control the motor normally so your problem is not EFI related.. more likely a mechanical problem.
So I know I have oil being sucked into the upper intake via PCV valve, which should be the primary cause of fouling the plugs. I haven't been able to fix that yet.
Today I disconnected the MAF meter after engine had been fully warmed up. It did not make a noticeable difference in the way engine ran or it's drivability. All it did was immediately throw the CEL Continuous Memory code 157, MAF sensor fault and 543 which had already been stored. 543 is Fuel Pump Secondary Circuit Fault. I think I'm getting that code from when I disconnected the fuel pump relay while performing engine compression test. I've tested both fuel pumps and FPR and all are within specs. Injectors are not leaking as it holds pressure after shutting engine off. The engine doesn't have a miss so I don't think any are clogged. What's left to test for the EFI? Is this engine stuck in limp mode because the O2 sensor is fouled?
So I know I have oil being sucked into the upper intake via PCV valve, which should be the primary cause of fouling the plugs. I haven't been able to fix that yet.
Today I disconnected the MAF meter after engine had been fully warmed up. It did not make a noticeable difference in the way engine ran or it's drivability. All it did was immediately throw the CEL Continuous Memory code 157, MAF sensor fault and 543 which had already been stored. 543 is Fuel Pump Secondary Circuit Fault. I think I'm getting that code from when I disconnected the fuel pump relay while performing engine compression test. I've tested both fuel pumps and FPR and all are within specs. Injectors are not leaking as it holds pressure after shutting engine off. The engine doesn't have a miss so I don't think any are clogged. What's left to test for the EFI? Is this engine stuck in limp mode because the O2 sensor is fouled?
Any and all help is greatly appreciated!
If you have the MAF sensor disconnected and there's no change in how the engine runs, then something else is amiss. If I disconnect mine, the engine dies.
I have another question. What MAF system are you using? Is this from a Mustang PCM and an overlay harness or later truck MAF PCM?
It's the original MAF system for this truck. It was a 302, all I did was swap in a 351. Computer, electrical harness, tranny, etc all the same as before.
I had to splice the O2 sensor wires to extend to new location for headers. If the wires were crossed up, or sensor is badly fouled, would it cause engine to always be in limp mode? Would it throw a code if no O2 sensor was detected?
It's the original MAF system for this truck. It was a 302, all I did was swap in a 351. Computer, electrical harness, tranny, etc all the same as before.
I had to splice the O2 sensor wires to extend to new location for headers. If the wires were crossed up, or sensor is badly fouled, would it cause engine to always be in limp mode? Would it throw a code if no O2 sensor was detected?
What year truck? I only know of '95 and later MAF equipped trucks.
And the 302 ran fine before this engine build and swap? No carry over electrical problems?
When you cut and spliced the O2 sensor wires, did you cut the harness from the engine bay and spliced or did you cut the actual O2 sensor wires? If you cut the O2 sensor wires, then this may very well be a problem. I've been told that it actually wrecks havoc on the sensor. I've bought O2 sensors with longer wiring just for long tube header's or custom exhaust.
It's a '94, apparently 1994 was when Ford started using MAF on their 302 equipped trucks. It had no known electrical problems prior to the swap, everything was in tip top shape.
I cut the actual O2 sensor wires. I purchased a brand new sensor when doing the swap. Headers were added with this swap and O2 sensor was about a half foot short of the bung on header collector. I used the old O2 sensor wires on the 302 to make the splice on the new sensor wires. The harness from the engine bay is unmolested. Perhaps a new O2 sensor with longer wires or extension is in order, I was not aware that cutting the sensor wires is a no-no. If this is the problem, then I am shocked it doesn't throw a code, but then again, I'm not familiar enough with how the computer is programmed to work.
It's a '94, apparently 1994 was when Ford started using MAF on their 302 equipped trucks. It had no known electrical problems prior to the swap, everything was in tip top shape.
I cut the actual O2 sensor wires. I purchased a brand new sensor when doing the swap. Headers were added with this swap and O2 sensor was about a half foot short of the bung on header collector. I used the old O2 sensor wires on the 302 to make the splice on the new sensor wires. The harness from the engine bay is unmolested. Perhaps a new O2 sensor with longer wires or extension is in order, I was not aware that cutting the sensor wires is a no-no. If this is the problem, then I am shocked it doesn't throw a code, but then again, I'm not familiar enough with how the computer is programmed to work.
Something electronic isn't correct. The MAF sensor being disconnected and not altering engine performance is the 1st clue.
Next I would pull the TPS and see what the engine does. Engine should have a high idle, elevated RPM but not more than 1500 rpm.
Then I would probably pull the PCM and inspect. The key issue seems electronic and the MAF sensor being disconnected with no change is a big clue.
Well pulling the O2 sensor does throw a code. I just disconnected it and it threw 172, HEGO sensor fault/lean. I don't know if this means its throwing the code based on sensor not being electrically connected only or if the sensor is indeed working and now it's throwing a code.
I'll do as you say in regards to the TPS sensor and PCM. Thanks again for your help!
Well pulling the O2 sensor does throw a code. I just disconnected it and it threw 172, HEGO sensor fault/lean. I don't know if this means its throwing the code based on sensor not being electrically connected only or if the sensor is indeed working and now it's throwing a code.
I'll do as you say in regards to the TPS sensor and PCM. Thanks again for your help!
Sounds like the O2 sensor is working. You can clean the sensor flutes, just be careful. I have used a fine brass brush gently to remove the black soot. Then you can install it and run it for a short time and see if it turns black with soot again.
When you pulled codes and retrieved the O2 code, did you also retrieve a code for the MAF sensor being disconnected?
Post back with your findings regarding the TPS and PCM.
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